perf: make command rbac-migrate-member-roles use less mem and make it…

[fatelei]

… fast

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Summary

make command rbac-migrate-member-roles use less mem and make it run fast

Screenshots

Before	After
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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	51.49%	51.50%	+0.00%
Strict coverage	51.01%	51.01%	+0.00%
Typed symbols	30,844	30,847	+3
Untyped symbols	29,331	29,331	0
Modules	2931	2931	0

[hjlarry]

LGTM